/*
 * Kodkod -- Copyright (c) 2005-present, Emina Torlak
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package kodkod.ast;

import java.util.Iterator;

import kodkod.ast.operator.ExprOperator;
import kodkod.ast.visitor.ReturnVisitor;
import kodkod.ast.visitor.VoidVisitor;
import kodkod.util.collections.Containers;

/**
 * A relational {@linkplain kodkod.ast.Expression expression} with more than two
 * children, composed with an nary {@linkplain ExprOperator operator}.
 *
 * @specfield op: ExprOperator
 * @invariant op.nary()
 * @invariant #children > 2
 * @author Emina Torlak
 */
public final class NaryExpression extends Expression implements Iterable<Expression> {

    private final ExprOperator op;
    private final int          arity;
    private final Expression[] children;

    /**
     * Constructs a new associative expression: op(children)
     *
     * @requires children array is not modified while in use by this associative
     *           expression
     * @requires some op.op[children]
     * @ensures this.children' = children && this.op' = op
     */
    NaryExpression(ExprOperator op, Expression[] children) {
        assert children.length > 2;
        if (!op.nary())
            throw new IllegalArgumentException("Cannot construct an nary expression using the non-nary operator " + op);

        this.op = op;
        this.children = children;

        switch (op) {
            case UNION :
            case INTERSECTION :
            case OVERRIDE :
                this.arity = children[0].arity();
                for (int i = 1; i < children.length; i++) {
                    if (children[i].arity() != arity)
                        throw new IllegalArgumentException("Incompatible arities: " + children[0] + " and " + children[i]);
                }
                break;
            case PRODUCT :
                int sum = 0;
                for (Expression child : children) {
                    sum += child.arity();
                }
                this.arity = sum;
                break;
            default :
                throw new IllegalArgumentException("Unknown associative operator: " + op);
        }
    }

    /**
     * Returns the arity of this associative expression.
     *
     * @return this.arity
     * @see kodkod.ast.Expression#arity()
     */
    @Override
    public final int arity() {
        return arity;
    }

    /**
     * Returns this.op.
     *
     * @return this.op
     */
    public ExprOperator op() {
        return op;
    }

    /**
     * Returns the number of children of this expression.
     *
     * @return #this.children
     */
    public int size() {
        return children.length;
    }

    /**
     * Returns the ith child of this associative expression.
     *
     * @requires 0 <= i < #this.children
     * @return this.children[i]
     */
    public Expression child(int i) {
        return children[i];
    }

    /**
     * Returns an iterator over this expression's children, in the increasing order
     * of indices.
     *
     * @return an iterator over this expression's children, in the increasing order
     *         of indices.
     */
    @Override
    public Iterator<Expression> iterator() {
        return Containers.iterate(children);
    }

    /**
     * {@inheritDoc}
     *
     * @see kodkod.ast.Expression#accept(kodkod.ast.visitor.ReturnVisitor)
     */
    @Override
    public <E, F, D, I> E accept(ReturnVisitor<E,F,D,I> visitor) {
        return visitor.visit(this);
    }

    /**
     * {@inheritDoc}
     *
     * @see kodkod.ast.Node#accept(kodkod.ast.visitor.VoidVisitor)
     */
    @Override
    public void accept(VoidVisitor visitor) {
        visitor.visit(this);
    }

    /**
     * {@inheritDoc}
     *
     * @see kodkod.ast.Node#toString()
     */
    @Override
    public String toString() {
        final StringBuilder s = new StringBuilder("(");
        s.append(child(0));
        for (int i = 1, size = size(); i < size; i++) {
            s.append(" ");
            s.append(op);
            s.append(" ");
            s.append(child(i));
        }
        s.append(")");
        return s.toString();
    }

}
